Comparative study on the selectivity of various spectrophotometric techniques for the determination of binary mixture of fenbendazole and rafoxanide Ahmed S. Saad a,⇑ , Ali K. Attia b , Manal S. Alaraki b , Eman S. Elzanfaly a a Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Kasr El-Aini Street, 11562 Cairo, Egypt b National Organization for Drug Control and Research (NODCAR), 6 Abu Hazem Street, Pyramids Ave, P.O. Box 29, Giza, Egypt highlights  Application of five different spectrophotometric methods.  Comparing selectivity of five spectrophotometric methods.  Simultaneous determination of fenbendazole and rafoxanide.  One way ANOVA statistical analysis for comparison of the proposed methods. graphical abstract article info Article history: Received 29 January 2015 Received in revised form 26 May 2015 Accepted 30 May 2015 Available online 4 June 2015 Keywords: Fenbendazole Rafoxanide First derivative Ratio derivative and difference Dual wavelength H-point standard addition method abstract Five different spectrophotometric methods were applied for simultaneous determination of fenbendazole and rafoxanide in their binary mixture; namely first derivative, derivative ratio, ratio difference, dual wavelength and H-point standard addition spectrophotometric methods. Different factors affecting each of the applied spectrophotometric methods were studied and the selectivity of the applied methods was compared. The applied methods were validated as per the ICH guidelines and good accuracy; specificity and precision were proven within the concentration range of 5–50 lg/mL for both drugs. Statistical anal- ysis using one-way ANOVA proved no significant differences among the proposed methods for the deter- mination of the two drugs. The proposed methods successfully determined both drugs in laboratory prepared and commercially available binary mixtures, and were found applicable for the routine analysis in quality control laboratories. Ó 2015 Elsevier B.V. All rights reserved. Introduction Fenbendazole (Fen) is methyl [5-(phenylsulfanyl)-1H-benzoim idazol-2-yl] carbamate, a white or almost white powder [1], used as an anthelmintic drug for the treatment of benzimidazole sus- ceptible mature and immature stages of nematodes and cistodes of the gastrointestinal and respiratory tracts of cattle and sheep [2]. Rafoxanide (Raf) is N-[3-chloro-4-(4-chlorophenoxy) phe nyl]-2-hydroxy-3,5-diiodo-benzamide [3]. It has an activity against fasciola hepatica in the mature and immature stages [2]. The mixture of Fen and Raf is formulated as oral suspension which is widely used as a veterinary broad spectrum anthelmintic. Literature survey revealed that several methods have been reported for determination of Fen in single component prepara- tions and in different mixtures. These include High performance and ultra-high performance liquid chromatography [1,4–6], densitometry [7], electrophoresis [8–10], voltammetry [11,12], http://dx.doi.org/10.1016/j.saa.2015.05.098 1386-1425/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 682–690 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa